A device for magnetic bearing of a rotor shaft with respect to a stator has the following features:    a) a first bearing part is connected to the rotor shaft and is surrounded by a second bearing part, which is associated with the stator, with a distance between them,    b) the first bearing part contains soft-magnetic rotor disk elements which are aligned at right angles to the axis of the rotor shaft, are arranged one behind the other in the direction of the axis and are each separated, forming an intermediate space,    c) the second bearing part contains soft-magnetic stator disk elements, which are aligned at right angles to the rotor shaft axis, are arranged one behind the other in the direction of the rotor shaft axis, are at a distance from one another and each project into one of the intermediate spaces of adjacent rotor disk elements,    d) a magnetic flux directed essentially in the axial direction is formed between the elements.
A corresponding bearing device is disclosed, for example, in DE 38 44 563.
Magnetic bearing devices allow non-contacting and wear-free bearing of moving parts. They require no lubricants and can be designed to have low friction.
Known radial and axial magnetic bearing devices use magnetic forces between stationary electromagnets of a stator and ferromagnetic elements which rotate jointly of a rotor body. The magnetic forces are always attractive in the case of this bearing type. In principle, this means that it is impossible to achieve an inherently stable bearing in all three spatial directions. Magnetic bearing devices such as these therefore require active bearing regulation, controlling the currents of electromagnets by position sensors and control loops and counteracting discrepancies of the rotor body from its nominal position. The multichannel regulation to be carried out requires complex power electronics. Corresponding magnetic bearing devices are used for example, for turbomolecular pumps, ultra-centrifuges, high-speed spindles for machine tools and X-ray tubes with rotating anodes; they are also known to be used for motors, generators, turbines and compressors.
The basic design of a corresponding bearing device 30 is sketched in FIG. 1. The figure shows two active radial bearings 31 and 32 with excitation magnets 33 and 34 and bearing rotors 35 and 36 on a rotor shaft 37, an active axial bearing 38 with rotor disks 39 and 40 on the rotor shaft 37 and concentric windings 42i on the rotor disks, as well as five distance sensors 41a to 41e corresponding to the in each case two lateral degrees of freedom per radial bearing and the single degree of freedom of the axial bearing. Furthermore, five associated control loops r1 to r4 and z5 are required. Because the attraction forces increase as the bearing gap becomes smaller in a bearing device such as this, corresponding devices are non-stationary from the start. The position of the rotor shaft 37 must therefore be stabilized by the control loops, comprising distance measurement by the sensors 41a to 41e with a downstream regulator and downstream amplifier, which feeds the excitation magnets 33 and 34. Corresponding bearing devices are accordingly complex. In addition, a mechanical holding bearing must be provided as a precaution against sudden failure of the control loop.
Magnetic bearing devices with permanent magnets and high-Tc superconductor material are also known, for example from DE 44 36 831 C2. Bearing devices such as these are intrinsically stable, that is to say they do not require regulation. However, because of the required cryogenic operating temperature for the superconductor material, in particular of below 80 K, thermal insulation and a refrigerant supply are required by an appropriate cryogenic coolant or by a refrigeration machine.
Bearing devices which are intrinsically stable in one direction with magnetic flux, soft-magnetic parts composed for example of iron and with permanent magnets are also known. In corresponding embodiments of bearing devices such as these, for example those which can be found in DE 34 08 047 A and DE 38 44 563 A, permanent-magnet rings on a shaft are aligned axially primarily with the poles of an iron yoke and thus provide radial centering. The magnetic flux is in this case amplified by excitation coils, with the axially unstable degree of freedom being stabilized, if necessary, by an electronic control loop. In this case, a plurality of stationary and rotating ring magnets which alternate axially one behind the other are arranged in a row with the same axial magnetization and carry out a radial bearing function. In this case as well, the axial degree of freedom must be actively stabilized.
DE 199 44 863 A also discloses a pump having a modified radial bearing. In this case, a rotor is provided with permanent-magnet cylinders instead of rings, with stationary permanent magnets or iron cylinders axially opposite one another on it. A stator which surrounds the rotor has electrical excitation coils. In addition, special radial stabilizers are provided.
All the bearing devices mentioned above and having permanent-magnet parts have relatively low supporting force and inadequate bearing stiffness, however.